Many state-of-the-art integrated circuits require the use of storage capacitors. For example, in dynamic random access memory (DRAM) devices, storage capacitors perform a vital data storing function. To enable DRAM and other devices become more highly integrated, techniques are required to increase the storage capacity of capacitors even as their lateral dimensions are reduced. Such techniques have included the use of capacitor dielectric materials having high dielectric strengths, such as tantalum pentoxide (Ta.sub.2 O.sub.5) and oxynitride (ON), because the capacitance of a capacitor is directly proportional to the magnitude of the dielectric strength of the dielectric material therein. Because the capacitance of a capacitor is also directly proportional to the surface area of the storage electrodes therein, storage electrodes having three-dimensional structures have also been developed. Examples of such capacitors include double-stacked, finned stacked, cylindrical, spread-stacked and box structure capacitors and hemispherically-grained (HSG) capacitors. Unfortunately, such three-dimensional structures may require complex fabrication steps and may be susceptible to fabrication defects which can limit long term reliability.
Other high dielectric materials have also been considered. Such high dielectric materials include barium strontium titanate (BST), lead zinconium titanate (PZT) and lead lanthanum zinconate titanate (PLZT). These materials have dielectric strengths that are much greater than other conventional dielectric materials. Unfortunately, these high dielectric materials may chemically react with conventional electrode materials (e.g., polysilicon) and degrade the electrical characteristics of capacitors formed thereby (e.g., increase leakage current). To address these limitations, additional electrode materials have been considered for compatibility with high dielectric materials such as BST, PZT and PLZT and silicon. These electrode materials include platinum (Pt), iridium (Ir), ruthenium (Ru), and ruthenium dioxide (RuO.sub.2), for example. The compatibility of these materials in lower electrodes of capacitors may be somewhat limited, however, because these materials may be susceptible to parasitic oxygen diffusion and such parasitic diffusion may degrade the electrical characteristics of regions adjacent these materials. To address these limitations, barrier layers have been considered as intermediate layers to be used between these electrode materials and surrounding capacitor regions (e.g., polysilicon conductive plugs). Nonetheless, oxidation of barrier layers can degrade the electrical characteristics of capacitors even if the barrier layers provide sufficient protection against oxygen diffusion.
Accordingly, techniques have also been considered which reduce the likelihood that such barrier layers will become oxidized in high dielectric capacitors. To illustrate, FIG. 1 provides a cross-sectional view of a conventional high dielectric integrated circuit capacitor. This capacitor comprises a semiconductor substrate 1 and an interlayer insulating layer 2 on the substrate 1. Conductive contact plugs 4 are also formed in the interlayer insulating layer 2 and these plugs 4 contact the semiconductor substrate 1. Each capacitor also includes a lower capacitor electrode 8, a high dielectric material 14 on the lower electrode 8 and an upper capacitor electrode 16 on the high dielectric material 14. A diffusion barrier layer 6 is also provided between the lower capacitor electrode 8 and the conductive contact plug 4. In addition, sidewall insulating spacers 9 are provided in recesses between the diffusion barrier layer 6 and the high dielectric material 14.
A conventional method of forming the integrated circuit capacitor of FIG. 1 is illustrated by FIGS. 2A-2B. In particular, FIG. 2A illustrates a structure having a diffusion barrier layer 6 and a lower capacitor electrode 8 on the diffusion barrier layer 6. As illustrated, the diffusion barrier layer 6 has been etched back so that its sidewalls are recessed relative to the sidewalls of the lower capacitor electrode 8. An oxidation barrier material 10 has also been deposited on the lower capacitor electrode 8 and this oxidation barrier material 10 fills the recesses between the sidewalls of the lower capacitor electrode 8 and the corresponding diffusion barrier layer 6. This oxidation barrier material 10 may comprise a material such as silicon nitride (SiN) or high density silicon dioxide (HD-SiO.sub.2).
In order to obtain good step coverage to completely fill the recesses, the oxidation barrier material 10 should be deposited at a relatively high temperature. However, such high temperature deposition can increase the rate of oxidation of the diffusion barrier layer 6. Deposition at a lower temperature can be used to reduce the likelihood of parasitic oxidation, however, such low temperature deposition may reduce the degree of step coverage and prevent the recesses from being completely filled. To address this problem, materials such as spin-on-glass (SOG) or flowable oxide (FOX) have been considered because they provide good step coverage even when deposited at low temperatures. But, as illustrated by FIG. 2B, removal of such oxidation barrier materials 10 using an etching technique may also result in a removal of some of the material comprising the lower electrode 8. If this occurs, the remaining oxidation barrier material may have an irregular pillar structure 11 at the end of etching and the thickness of the resulting sidewall spacers 10a may be nonuniform. Both of these defects can lead to a degradation in the reliability and performance characteristics of the capacitors.
Referring now to FIGS. 3A-3B, another conventional method of forming integrated circuit capacitors is illustrated. This method is similar to the method of FIGS. 2A-2B, however, an aluminum oxide (Al.sub.2 O.sub.3) material is used as the oxidation barrier layer 12 because it has good step coverage even when deposited at low temperatures. Unfortunately, as illustrated by FIG. 3B, because aluminum oxide may have poor etching selectivity relative to many of the materials used to form the lower capacitor electrode 8, the resulting lower capacitor electrode 8a may have significantly reduced surface area after the oxidation barrier layer 12 has been etched-back. In addition, the remaining sidewall spacers 12a may have large lateral dimensions which may limit integration density.
Thus, notwithstanding these above-described methods of forming integrated circuit capacitors, there still continues to be a need for improved integrated circuit capacitors and methods of forming same.